The presently known warning systems on vehicles, particularly large earth moving type vehicles, namely the off-the-road rubber tired machinery such as road scrapers, front end loaders and the like, is unsatisfactory in that there is a lack of automatic equipment which will effect a maintenance of the hydraulic system in operable condition should there be a failure in the primary pumping system or driving mechanism therefor. The presently known systems have usually three methods to warn the operator of a primary pump failure. One type of warning system is a buzzer which warns the operator that there is a failure in the primary steering system. The second type of warning system is a red light which is supposed to be noticed by the operator to warn him of a primary steering failure. The third type of warning system is the operator's inability to steer the vehicle. In all three instances, the operator must manually operate a switch to turn on an emergency pumping system to reactivate the hydraulics to supply power to the primary steering system. In some cases, the operator will panic as a result of events happening too fast for him to remember to manually activate the switch and, as a result, an accident is a highly likely occurrence, Accordingly, it is desirable to have an automated control which automatically effects a utilization of fluid from an emergency pumping system when the flow of fluid from the primary pumping system falters.
At present, there are three types of drive systems for the emergency pumps. There are D.C. motor driven emergency pumps which become electrically activated to supply fluid into the primary fluid circuit when the primary pump fails or the driving mechanism therefor stops. The D.C. motor driven emergency pump is electrically activated by either a pressure switch or a flow sensing switch. Another type of drive for emergency pumps is the provision of a ground engaging wheel provided on the vehicle or a transmission device which is driven from the rear axle or gear box and operates only when the vehicle is in motion. As the vehicle starts to move and drive the auxiliary pump, the flow of fluid caused by the primary pump dictates whether the emergency pump flow is required. A relief valve is utilized in the system to dump the emergency pump flow back into the reservoir when it is not needed and to effect a utilization of the flow from the emergency pump when the flow from the primary pump is too low to maintain a proper control of the vehicle. A still further type of drive or control for emergency purposes is the provision of an accumulator system which utilizes an accumulator in the fluid circuit to store energy which can be called upon at a later time if the primary pump or engine drive therefor fails. This system is obviously very limited in time because of the limited capacity of the accumulator.
My U.S. Pat. No. 3,923,423 relates to a valve wherein the auxiliary pump is normally off and is electrically operated in response to an insufficient fluid flow from the primary pump. I have designed a new valve for use in systems wherein the emergency pump is continuously driven either by an electrical motor to which electrical energy is supplied by the vehicle battery and/or electrical generating system or is driven by a ground engaging wheel or by a transmission device connected to the rear axle and is operative only when the vehicle is in motion.
Accordingly, it is an object of this invention to provide a valve for automatically controlling the utilization of the fluid from an emergency pumping system, which is operated only when the vehicle is in motion, when the flow rate of the fluid from the primary pumping system is slightly less than the flow rate through the valve at engine idle speed where the engine is utilized to drive the primary pumping system. It is a further object of this invention to provide a valve which is compact and which will be utilizable in existing systems with a minimum of installation considerations. It is a further object of this invention to provide a valve which is easily manufactured and at a minimum of cost and is easily maintained in satisfactory operating conditions. It is a further object of this invention to provide a valve which is operable with a minimum of pressure surges and pressure differentials occurring in the line.